The Rugby time signal has scheduled outages every few months. On 11 June 2009, I used a software radio to record the radio spectrum around the time of the outage, and then produced an animation of the result (warning 48MB).
This was done by taking 10s spectrum samples every 100s, so the notched horizontal line at 60MHz is the MSF signal. It looks like they turned it off pretty promptly around 10:00, and then back on again about 12:00. They also did two quick switch offs later before 14:00.
I also took a plot of the reachability reported by my NTP server. Since I poll every 32s, sampled every 30 and MFS only provides a date every 60s, so I can't have a reachability much about 50%). It seems to line up pretty well with the spectrogram animation.